1. Field of the Invention
The present disclosure relates to a resistance heated sapphire single crystal ingot grower, a method of manufacturing a resistance heated sapphire single crystal ingot, a sapphire single crystal ingot, and a sapphire wafer.
2. Description of the Related Art
Demands on sapphire wafers used as a substrate for a light emitting diode (LED) using a nitride semiconductor, e.g., gallium nitride (GaN), have increased and the sapphire wafers are in the spotlight because of high mass productivity in comparison to other substrates.
According to typical techniques, a growth furnace charged with a high-purity alumina (Al2O3) raw material is heated at about 2100° C. or more to melt the raw material, and a sapphire wafer is then fabricated through performing a series of grinding and polishing processes, such as coring, grinding, slicing, lapping, heat treatment, and polishing, on an ingot boule grown as a single crystal by using various methods such as a Czochralski method (hereinafter, referred to as a “CZ method”), a Kyropoulos method, an edge-defined film-fed growth (EFG) method, and a vertical horizontal gradient freezing (VHGF) method.
A crystallographic orientation of a sapphire substrate currently in mass production having relatively excellent LED light conversion efficiency characteristics is C-axis, and although there is a possibility that the crystallographic orientation thereof may be changed in the future, differences in yields of utilizing single crystals grown according to the growth methods of an ingot boule do not change. The differences in the yields will be depend on physical and chemical properties of a sapphire single crystal and characteristics according to the crystal growth methods.
Meanwhile, with respect to the growth of a sapphire ingot, the CZ method is an excellent method in terms of the yield of a single crystal, in which a crystallographic orientation of a substrate used is the same as a growing orientation of the crystal.
FIG. 1 an exemplary view illustrating a method of manufacturing a sapphire single crystal ingot IG by using a typical induction heated CZ method.
A sapphire ingot grower 10 using a typical CZ method by means of induction heating includes a RF-coil 30, an iridium (Ir) crucible 20, and a crucible support (not shown).
The RF-coil 30 generates induction current on a surface of the Ir-crucible 20 while the direction of high-voltage current flow changes at a radio frequency.
The Ir-crucible 20 generates heat caused by stress on the surface of the crucible due to the changes in the direction of induction current flow and acts as a molten bath containing high-temperature molten alumina (Al2O3).
However, with respect to a method of growing a c-axis sapphire single crystal ingot by using a typical induction heated CZ method, first, qualities of the sapphire single crystal may deteriorate according to the use of an Ir-crucible in the typical induction heated CZ method, and second, large size and large scaling of the sapphire single crystal ingot may be difficult according to the use of an Ir-crucible in the typical induction heated CZ method, and limiting factors may greatly affect the use of an insulation material and external field resources may not be utilized.
First, limitations in the quality deterioration of the sapphire single crystal according to the use of an Ir-crucible in the typical induction heated CZ method are described below.
In the typical induction heated CZ method, since the Ir-crucible directly generates heat, control of the temperature distribution of high-temperature molten alumina may be difficult and bubbles may be generated by localized heating.
Also, in the typical induction heated CZ method, smooth discharge of the generated bubbles may not be facilitated because free convection (FC) cells are strong as shown in FIG. 1.
In the typical induction heated CZ method, since stress may be generated between a growth interface of a c-axis sapphire single crystal facet surface and a melt while the growth interface becomes convex downward by means of FC cells, crystallographic characteristics, and latent heat effects of high-temperature alumina, crystal defects such as core facets, inclusions, etched pit dislocations (EPD), and striations may be generated.
Also, in the typical CZ method using induction heating, since a free convection cell (FC-cell) caused by the induction heating may exhibit very complex turbulence characteristics (the so-called “Rayleigh-Benard convection”) behavior, constant heat and mass transfer at the growth interface may be difficult. Therefore, dislocation density may be very high and the growth of a bubble free perfect single crystal may be difficult.
In the typical induction heated CZ method, changes in the convection cells of a high-temperature alumina melt may not be induced because the Ir-crucible acting as a heating element may not be rotated or lifted.
Further, in the typical induction heated CZ method, the solidification latent heat effect of the growth interface may make the growth interface convex toward the melt due to the FC-cells. As a result, when the grown ingot is strongly rotated, crystal defects may be induced by the application of large shear stress caused by friction according to high viscosities of the growth interface and the melt.
Second, limitations in the difficulties of obtaining large size and large scaling of the sapphire single crystal ingot according to the use of an Ir-crucible in the typical induction heated CZ method, and the limiting factors with respect to the use of an insulation material and limitations of not being able to utilize the external field resources are described below.
For example, iridium, a raw material for the Ir-crucible, is a very limited material, and large size and large scaling of iridium for growing a single crystal having a diameter of 150 mm or more are difficult.
Also, according to the use of a RF-coil, the typical induction heated CZ method has limitations in that maintenance costs of the RF-coil and electricity cost may be large and the fabrication of the RF-coil may be difficult as well as high costs being required.
Further, in the typical induction heated CZ method, since the induction current is generated in a magnetic field coil in addition to the crucible, the external field resources such as magnetic field and electromagnetic field may not be utilized.